The present invention relates to magnetic devices having magnetic features and methods of fabricating the magnetic features. In particular, the present invention relates to magnetic devices having magnetic features for use in magnetic writers and magnetic random access memory cells, and methods of fabricating the magnetic features with chemical-mechanical polishing.
Magnetic writers used with hard drives incorporate a variety of magnetic devices having magnetic features. Examples of such magnetic devices include poles, yokes, coils, and contact plugs. Magnetic random access memory (MRAM) incorporates magnetic features for magnetic storage cells. In contrast to dynamic random access memory, which requires continuous supply of electricity, MRAM is a solid-state, non-volatile memory that uses magnetism rather than electrical power to store data.
Magnetic devices having magnetic features for use magnetic writers and MRAM cells are required to be small, generally smaller than conventional semiconductor features. The magnetic features must also have accurate dimensions, which leads to difficulties in consistent fabrication of the magnetic features due to the small sizes. Fabrication of magnetic features for magnetic devices typically includes depositing and patterning various layers of material, and subsequently removing excess material via polishing techniques, such as chemical-mechanical polishing (CMP).
CMP is used to remove surface topography in order to achieve planar surfaces suitable for photolithographic patterning of complex patterns. Material is removed during a CMP process by a combination of chemical etching and mechanical abrasion. CMP processes typically have a material removal rate of 300 to 500 nanometers (nm) per minute under normal process conditions. Removal continues until an endpoint is reached, which is theoretically the point where all of the excess material is removed, and a smooth planar surface remains. Planarized surfaces are required for creating magnetic devices for magnetic writers and MRAM cells, and for subsequent photolithography steps.
The CMP endpoint may be determined by a variety of techniques. For example, prior CMP processes have incorporated instruments to measure changes in the surface optical reflectivity, changes in the surface temperature, and changes in eddy currents induced through the layers. Other CMP processes alternatively use prior test runs to estimate polish time to the endpoint. However, these prior CMP endpoint detection techniques are subject to variations as to when the endpoints are detected. This variation, defined in terms of under-polishing and over-polishing, reduces consistency between wafer thicknesses. While these prior CMP endpoint detection techniques may be adequate for semiconductor features, such semiconductor features are larger than magnetic features required for magnetic writers and MRAM cells. In fact, these prior techniques for detecting CMP endpoints can have endpoint variations exceeding the total thickness of magnetic features required for magnetic writers and MRAM cells. Thus, there is a need in the industry for a process capable of accurately detecting CMP endpoints for fabricating consistent and accurate magnetic features.